Imaging systems of various designs have been used extensively for generating images. Exemplary imaging systems include copiers, scanners, cameras, and more recently digital cameras, and other devices capable of generating images. Color imaging systems have also experienced significant improvements and are increasing in popularity. Color imaging systems may be calibrated to increase accuracy of various image processing algorithms (e.g., illuminant estimation, color correction, etc.), and also to increase the color accuracy of final reproductions.
For example, even identically configured imaging systems may vary from one another due to product tolerances or design variances. Referring to FIG. 1, a graphical representation of relative responsivity versus wavelength is shown for two hundred digital cameras corresponding to the same product. FIG. 1 illustrates the variations in blue, green, and red sensor responsivities of the sampled cameras represented by respective bands 4, 6 and 8. The illustrated bands have widths illustrating the size of the variations between respective cameras although the cameras structurally comprise the same components.
One color calibration technique uses reflective charts. Reflective charts can be utilized to calibrate a camera quickly and they are relatively inexpensive. However, calibrations implemented using reflective charts may not be accurate enough for utilization with cameras. Monochromators, on the other hand, can produce very accurate calibrations of color imaging systems including cameras. However, the calibration procedure with monochromators may take a relatively long period of time to complete, the devices are expensive, and accurate and controlled lighting is typically used.
Other analysis systems emit light of different wavelengths for use in performing analysis of an imaging device. The emitted light is captured by an imaging device in one or more images. Image data resulting from the captured images and information regarding the emitted light may be utilized to determine a responsivity function of the imaging device. However, some calculation techniques result in determination of a responsivity function including return of both positive as well as negative values (e.g., usage of the pseudo-inverse of spectral data of a calibration chart and raw camera responses). The negatives values are typically clipped to zero which may introduce error into the calculated responsivity function of the imaging device with respect to the true responsivity of the imaging device.
At least some aspects of the disclosure are related to improved methods and systems for analyzing an imaging device.